On Jan 31, 2008 2:13 PM, Bulat Ziganshin
Hello Johan,
Thursday, January 31, 2008, 2:35:06 PM, you wrote:
* Those who do text I/O. We might want to add an encoding parameter to those or add other, identical functions that takes the encoding as a parameter and use a default encoding for the functions that lack explicit encoding. e.g.
readFile :: FilePath -> IO String -- defaults to some encoding readFileWithEnc :: Encoding -> FilePath -> IO String -- explicit encoding, should have a better function name
i can quickly tell why it's bad idea. it doubles amount of i/o functions just for this particular need. then you will notice that we also need functions which don't lock Handle or add some other processing and number of functions will double again and again
i don't even say that for practical programming you will quickly find that passing encoding for particular file down all the functions that work with it is a nightmare
the right way to deal with "modifiers" is to attach them to the Handle itself like this:
f <- openFile "name" >>= withLocking >>= withEncoding utf8
and now look at http://haskell.org/haskellwiki/Library/Streams ;)
data Encoding = Ascii | Utf8 | Utf16 -- no ALL CAPS pretty please!
btw, it's another bad idea which means that set of encodings cannot be changed without changing library. it will be especially "great" if we will hard-code this into base, meaning that in order to get support for new encodings you should upgrade your ghc and any new encodings will become available for ghc users ONE YEAR AFTER actual implementation
in FP language, the best way to provide encoding is to define it as pair of functions:
data Encoding = Encoding { encode :: String -> String , decode :: String -> String }
utf8 = Encoding encodeUtf8 decodeUtf8
Just to be clear here. I don't care (for the purpose of this email) what these functions will look like. I just provided some random examples. I was asking how changes to existing functions would be handled. It's interesting to hear your ideas on the topic none the less. :) -- Johan